Image processing apparatus for variably magnifying image and controlling image density

Abstract

An image forming apparatus capable of magnifying a target image to any desired magnification, includes functions for detecting the maximum and minimum densities from limited image information, including a data piece representing a picture element of the target image, functions for determining from the difference between the maximum and minimum densities detected by the detection means, whether the picture element is in a photographic region or a character region, functions for determining a picture element density appropriate for magnifying the target image from the density of the target picture element and that of a picture element close to the target picture element, and functions for outputting the picture element density determined by the density-determining means, in accordance with whether the target picture element is in a photographic region or a character region.

What is claimed is: 
     
       1. An image forming apparatus capable of magnifying a target image at any desired magnification, comprising: means for detecting maximum and minimum densities from image information in a predetermined area including a target picture element of the target image;   means for determining, from the difference between the maximum and minimum densities detected by the detection means, whether the picture element is in a photographic region or a character region;   means for determining a picture element density appropriate for magnifying the target image, from the density of the target picture element and that of a picture element close to the target picture element;   means for outputting the picture element density determined by the density-determining means, in accordance with whether the target picture element is in a photographic region or a character region; and   means for comparing the picture element density determined by the density-determining means with first and second reference densities, and for selecting the maximum density when the density determined by the density-determining means is higher than the first reference density, selecting the minimum density when the density determined by the density-determining means is lower than the second reference density, and selecting an average of the maximum density and the minimum density when the density determined by the density-determining means is lower than the first reference density and higher than the second reference density,   wherein the output means outputs the density determined by the density-determining means when the region-determining means determines that the target picture element is in the photographic region, and outputs the density selected by the density-selecting means when the region determining means determines that the target picture element is in the character region.   
     
     
       2. An image forming apparatus capable of magnifying a target image at any desired magnification, comprising: means for detecting maximum and minimum densities from image information in a predetermined area including a target picture element of the target image;   means for determining, from the difference between the maximum and minimum densities detected by the detecting means, whether the picture element is in a photographic region or a character region;   means for determining a picture element density appropriate for magnifying the target image, from the density of the target picture element and that of a picture element close to the target picture element;   means for outputting the picture element density determined by the density-determining means, in accordance with whether the target picture element is in a photographic region or a character region; and   means for comparing the picture element density determined by the density-determining means with an average of the maximum and minimum densities, and for selecting the maximum density when the density determined by the density-determining means is higher than the average of the maximum and minimum densities, and selecting the minimum density when the density determined by the density-determining means is lower than the average of the maximum and minimum densities,   wherein the output means outputs the density determined by the density-determining means when the region-determining means determines that the target picture element is in the photographic region, and outputs the density selected by the density-selecting means when said region-determining means determines that the target picture element is in the character region.   
     
     
       3. An image forming apparatus capable of magnifying a target image at any desired magnification, comprising: means for detecting maximum and minimum densities from image information in a predetermined area including a target picture element of the target image;   means for determining, from the difference between the maximum and minimum densities detected by the detection means, whether the picture element is in a photographic region or a character region;   means for determining a picture element density appropriate for magnifying the target image, from the density of the target picture element and that of a picture element close to the target picture element;   means for outputting the picture element density determined by the density-determining means, in accordance with whether the target picture element is in a photographic region or a character region; and   means for comparing the picture element density determined by said density-determining means with an average of the maximum and minimum densities, and selecting the minimum density, when the density determined by the density-determining means is lower than the average of the maximum and minimum densities,   wherein the output means outputs the density determined by the density-determining means when the region-determining means determines that the target picture element is in the photographic region, outputs the density of the target picture element when the region-determining means determines that the target picture element is in the character region and when the difference between the maximum density and the minimum density is equal to or more than a predetermined value, and outputs the density selected by said density-selecting means when the region-determining means determines that the target picture element is in the character region and when the difference between the maximum density and the minimum density is less than the predetermined value.   
     
     
       4. An image forming apparatus capable of magnifying a target character image to any desired magnification, comprising: means for detecting maximum and minimum densities from image information in a predetermined area including a target picture element of the target character image;   means for determining a picture element density appropriate for magnifying the target character image, from the density of the target picture element and that of a picture element close to the target picture element;   means for comparing the picture element density determined by the density-determining means with first and second reference densities; and   means for selecting the maximum density when the density determined by the density-determining means is higher than the first reference density, selecting the minimum density when the density determined by the density-determining means is lower than the second reference density, and selecting an average of the maximum density and the minimum density when the density determined by the density-determining means is lower than the first reference density and higher than the second reference density.   
     
     
       5. An image forming apparatus capable of magnifying a target character image to any desired magnification, comprising: means for detecting maximum and minimum densities from image information in a predetermined area including a target picture element of the target character image;   means for determining a picture element density appropriate for magnifying the target character image, from the density of the target picture element and that of a picture element close to the target picture element;   means for comparing the picture element density determined by the density-determining means with an average of the maximum and minimum densities; and   means for selecting the maximum density when the density determined by the density-determining means is higher than the average of the maximum and minimum densities, and selecting the minimum density when the density determined by the density-determining means is lower than the average of the maximum and minimum densities.   
     
     
       6. An apparatus according to claim 4, wherein the density-determining means further comprises means for linearly interpolating the density of the target picture element and that of the picture element close thereto. 
     
     
       7. An apparatus according to claim 5, wherein the density-determining means further comprises means for linearly interpolating the density of the target picture element and that of the picture element close thereto.